Increasing the ion-exchange capacity of MFI zeolites by introducing Zn to aluminosilicate frameworks.

MFI zeolites exchanged with various cations have gained a great deal of attention as catalysts. Increase in the ion-exchange capacity of zeolites can improve their catalytic properties by introducing more active sites; however, the ion-exchange capacity of MFI zeolites is limited by maximum aluminum content in the structure. To improve the ion-exchange capability of the MFI zeolites beyond the upper limit of the aluminosilicate MFI zeolites, we propose herein an approach to incorporate Zn(ii) in the zeolitic framework, because Zn in the framework sites generates two negative charges per atom. Using zincoaluminosilicate gels prepared via co-precipitation, organic-free synthesis of zincoaluminosilicate MFI zeolites was achieved. The obtained zincoaluminosilicate MFI zeolites had high Zn contents comparable to those in the initial zincoaluminosilicate gels with both Zn and Al in the zeolite framework. In contrast, the use of conventional sources of Si, Al, and Zn resulted in zeolites with extra-framework zinc oxide species. The obtained Zn-substituted MFI zeolites were shown to possess higher ion-exchange capacity compared to aluminosilicate MFI zeolites. It was also revealed that the zincoaluminosilicate MFI zeolites have high affinity for the divalent cation compared to the aluminosilicate analog, likely due to the two negative charges in close proximity. Because of these higher ion-exchange efficiencies, especially for divalent cations, the obtained zincoaluminosilicate MFI zeolites are expected to be efficient platforms for several important catalytic reactions.

Organic-free synthesis of zincoaluminosilicate zeolites from homogeneous gels prepared by a co-precipitation method.

Zeolites containing Zn in their frameworks are promising materials for ion-exchange and catalysis because of their unique ion-exchange capabilities and characteristic Lewis acidity. However, expensive organic compounds often required in their synthesis can prevent their practical uses. Here, a facile organic-free synthesis route for new zincoaluminosilicate zeolites having MOR topology, in which both Zn and Al are substituted in the framework, is demonstrated for the first time. The use of homogeneous zincoaluminosilicate gels prepared by a co-precipitation technique as raw materials is vital for the successful incorporation of both Zn and Al into the zeolite frameworks as revealed by several characterization techniques including solid-state NMR and UV-vis spectroscopy, and ion-exchange experiments. The obtained zincoaluminosilicate zeolites had high Zn contents comparable to those in the initial zincoaluminosilicate gels. In contrast, the uses of conventional sources of Si, Al, and Zn resulted in zeolites with very low contents of framework Zn or zeolites with extra-framework zinc oxide-species. FT-IR measurements using probe molecules and ion-exchange experiments suggested that there are two different environments of Zn in the zeolite frameworks. The obtained zincoaluminosilicate zeolites showed a higher ion-exchange efficiency for divalent cations such as nickel compared to the aluminosilicate analog. It is expected that the present co-precipitation technique is efficient for the incorporation of Zn (and other metals) into a variety of zeolite frameworks. To show its extended applicable scope, the synthesis of zincoaluminosilicate *BEA zeolite is also demonstrated.

Seed-Assisted Synthesis of MWW-Type Zeolite with Organic Structure-Directing Agent-Free Na-Aluminosilicate Gel System.

The seed-assisted synthesis of zeolites without using organic structure-directing agents (OSDAs) has enabled alternative routes to the simple, environmentally friendly and low-cost production of industrially important zeolites. In this study, the successful seed-assisted synthesis of MCM-22 (MWW-type) zeolite with an OSDA-free gel is reported for the first time. MWW-type zeolites are obtained by the addition of as-synthesized MCM-22 seeds prepared with hexamethyleneimine (HMI) into OSDA-free Na-aluminosilicate gels. Based on the results of XRD, ICP-AES, NMR, N2 physisorption and NH3 -TPD, the product exhibited different features compared to those of the seeds. The H-form product can serve as a catalyst in Friedel-Crafts alkylation reaction of anisole with 1-phenylethanol, and its catalytic activity is comparable to the seeds. Furthermore, XRD, FE-SEM, TG-DTA, CHN, FT-IR and NMR analyses of products and intermediates provide insights into the role of seeds and occluded HMI, the crystallization process, and key factors for achieving seed-assisted synthesis of MWW-type zeolites with an OSDA-free gel system. The present results provide a new perspective for the economical and environmentally friendly production of MWW-type zeolites.

Ultratrace Measurement of Acetone from Skin Using Zeolite: Toward Development of a Wearable Monitor of Fat Metabolism.

Analysis of gases emitted from human skin and contained in human breath has received increasing attention in recent years for noninvasive clinical diagnoses and health checkups. Acetone emitted from human skin (skin acetone) should be a good indicator of fat metabolism, which is associated with diet and exercise. However, skin acetone is an analytically challenging target because it is emitted in very low concentrations. In the present study, zeolite was investigated for concentrating skin acetone for subsequent semiconductor-based analysis. The adsorption and desorption characteristics of five zeolites with different structures and those hydrophobicities were compared. A hydrophobic zeolite with relatively large pores (approximately 1.6 times larger than the acetone molecule diameter) was the best concentrator of skin acetone among the zeolites tested. The concentrator developed using zeolite was applied in a semiconductor-based gas sensor in a simulated mobile environment where the closed space was frequently collapsed to reflect the twisting and elastic movement of skin that would be encountered in a wearable device. These results could be used to develop a wearable analyzer for skin acetone, which would be a powerful tool for preventing and alleviating lifestyle-related diseases.

Seed-assisted, one-pot synthesis of hollow zeolite beta without using organic structure-directing agents.

Hollow aluminosilicate zeolite beta was successfully synthesized by adding CIT-6, that is, zincosilicate zeolite, which has the same topology as beta, as seeds to the Na-aluminosilicate gel without the need for organic structure-directing agents. One important factor in the successful organic structure-directing agent (OSDA)-free synthesis of hollow beta crystals is the solubility of the seed crystals in alkaline media. CIT-6 was less stable than aluminosilicate zeolite beta in alkaline media and the solubility changed depending on whether the crystals were calcined or not. The hollow beta could be obtained by using the uncalcined CIT-6 seed crystals. The volumes of intra-crystalline voids were tuned by changing the reaction time and the initial gel compositions, such as the SiO2/Al2O3 and Na2O/SiO2 ratios. We estimated that the intra-crystalline voids were formed through the dissolution of the seed crystals, just after the crystal growth of new beta on the outer surface of the seeds. In addition, new crystal growth toward inside of the void was also observed by TEM. On the basis of the characterization data, such as chemical analysis, N2-adsorption/desorption measurements, and TEM observation, a formation mechanism of the intra-crystalline voids is proposed and discussed.

A working hypothesis for broadening framework types of zeolites in seed-assisted synthesis without organic structure-directing agent.

Recent research has demonstrated a new synthesis route to useful zeolites such as beta, RUB-13, and ZSM-12 via seed-assisted, organic structure-directing agent (OSDA)-free synthesis, although it had been believed that these zeolites could be essentially synthesized with OSDAs. These zeolites are obtained by adding seeds to the gels that otherwise yield other zeolites; however, the underlying crystallization mechanism has not been fully understood yet. Without any strategy, it is unavoidable to employ a trial-and-error procedure for broadening zeolite types by using this synthesis method. In this study, the effect of zeolite seeds with different framework structures is investigated to understand the crystallization mechanism of zeolites obtained by the seed-assisted, OSDA-free synthesis method. It has been found that the key factor in the successful synthesis of zeolites in the absence of OSDA is the common composite building unit contained both in the seeds and in the zeolite obtained from the gel after heating without seeds. A new working hypothesis for broadening zeolite types by the seed-assisted synthesis without OSDA is proposed on the basis of the findings of the common composite building units in zeolites. This hypothesis enables us to design the synthesis condition of target zeolites. The validity of the hypothesis is experimentally tested and verified by synthesizing several zeolites including ECR-18 in K-aluminosilicate system.

Critical factors in the seed-assisted synthesis of zeolite beta and "green beta" from OSDA-free Na+-aluminosilicate gels.

Organic structure-directing agent (OSDA)-free synthesis of zeolite beta is a subject of both scientific and industrial interest. Herein, we report a comprehensive investigation into the effects of various parameters on the seed-assisted crystallization of zeolite beta in the absence of OSDA. The crystallization behavior of "OSDA-free beta" is strongly governed by the chemical composition of the starting Na(+)-aluminosilicate gel as well as by the Si/Al ratios of the calcined beta seed crystals, which are prepared using tetraethylammonium hydroxide (TEAOH). Furthermore, OSDA-free beta seed crystals can be used to form zeolite beta, termed "green beta". XRD, scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy, and ²7Al magic angle spinning NMR analyses showed that the OSDA-free beta and green beta were of high purity and crystallinity. The nitrogen adsorption-desorption of OSDA-free beta and green beta revealed higher surface areas and larger volumes in the micropore region than those of the beta seeds synthesized with OSDA after calcination. These results provide a robust and reliable process for the environmentally friendly production of high-quality zeolite beta in a completely OSDA-free Na(+)-aluminosilicate system.

RMA-3: synthesis and structure of a novel Rb-aluminosilicate zeolite.

RMA-3 (Rubidium Microporous Aluminosilicate-3) was hydrothermally synthesized from rubidium-aluminosilicate gels without using any organic or inorganic additives, and its structure determined by XRD Rietveld analysis was confirmed as a novel framework topology containing two 8-membered ring pore-openings with dimensions of 0.49 x 0.37 nm and 0.34 x 0.38 nm.